Packing Gland Blues - or - why am I so stupid after 23 years?

[TacomaSailor]

Our boat’s packing gland/prop shaft runs nice and cool for extended periods with 30-drops per minute coming thru. After shutting the engine down at the dock the 30-drops per minute continues and the packing gland cools to ambient water temp within an hour. Then after a few days of non-use, the packing gland goes bone dry.

OR - Why does the packing gland run at ambient water temp + 30 F for hours and hours and then suddenly jump to 170 F while still running?

I’ve owned my boat since I purchased her new in February 1995. We’ve put 2,950 hours on the engine. Only I, my brother, and one other trusted mechanic have ever worked on the engine, transmission, prop, packing gland, strut, cutlass bearing, and prop.

I’ve cleaned and repacked the packing gland many times. But, during the last four years and 150 hours of engine use I’ve encountered endless and baffling packing gland/prop shaft overheat problems.

During the first 17-years and 2,800 hours the shaft and packing gland ran at a constant temperature equal to water ambient + 20 to 30 degrees F. That was in 44 F cold water at 52 degrees N and 92 degree warm water at 18 degrees N and everywhere in between. I set the packing gland to drip one drop every 10-seconds during that 2,800 hours of cool operation.

Since 2013 I’ve been cleaning-packing-repacking-cleaning etc with no resolution to unexplained shaft/gland overheating. The problem is that the shaft and packing gland run at normal temperature for hours and then suddenly heat up to 150 - 170 degree F.

The cause seems to be a SUDDEN decrease in water flow thru the packing gland. However, when I remove the packing nut from the shaft log the water streams in past the shaft at about 4 gallons per hour. It is a steady stream with no bubbles or spurts.

For example:
Two months ago I motored at 2700 RPM for an hour and the packing gland/shaft (PGS) stayed below 90 degrees in 68 degree water. The packing material had been in the packing nut for 18-months and 50-hours of engine use with no overheating problems.

A month later, with no intervening engine operation, the PGS heated to 170 degrees in 72 degree water after 30-minutes engine run time. The packing gland/lock nut had not moved relative to each other. I mark them when I set them and then check that they have not moved after each time I run the engine. Upon docking I was able to see that NO water at all was flowing thru the packing material or around the shaft.

Recently I carefully and thoroughly cleaned ALL old PTFE flax out of the packing nut and put in two (2) carefully cut wraps of new ¼” PTFE flax packing. I tightened the packing nut down so there were 60-drops per minute (DPM) coming thru the packing while the shaft was not turning. I ran the engine in FWD at 2,400 RPM (6.8 knots in still water) for 10-minutes and the PGS stayed below 90 degrees in 73 degree ambient water. After shutting down the engine I found 40-dpm coming thru the packing.

The next day I noticed 30-dpm coming thru the shaft/packing. I again ran the engine at 2,400 RPM for 3-minutes in FWD and found the packing nut and shaft hit 110 degrees. I shut the engine down and ten minutes later found NO water at all coming thru the packing nut or around the shaft. I verified the packing nut and lock nut were in the same relative position to each other and had not moved on the shaft log.

I removed the packing nut from the shaft log the water streamed in past the shaft at about 4 gallons per hour. It was a steady stream with no bubbles or spurts.

I reset the nuts to get 40-drops per minute, ran the engine as before and never saw more than 92 degrees in 74 degree ambient water. I shut the engine down and let it cool for an hour. I then climbed into the prop shaft compartment and counted 30-drops per minute coming thru the packing and around the shaft.

I again ran the engine up to 2,600 RPM for 10-minutes and the packing gland/shaft stayed below 96 degrees. Half an hour after shutting down the engine my brother verified that 30-drops per minute were coming thru the packing and the nut had cooled to 80 degrees.

Two days later I returned to the boat and checked the packing gland and locknut. They had not moved on the shaft log or relative to each other BUT not a single drop of water was coming thru the packing material or around the shaft and the floor under the prop shaft and packing gland was bone dry.

This is the pattern that has been repeating thru three re-packings in the last four years.

During that time I have also done the following:

Replaced the 1.25” prop shaft
Replaced prop shaft coupling
Replaced cutlass bearing
A superb machinist measured new propshaft runout to be less than .0005”
Verified coupling face gap is within .001” at eight points around the coupling


WHY does the water flow thru the packing material disappear after a few days of non-usage?

[Diesel Bill]

Hi TacomaSailor, I've been through the same thing after repacking many pumps in the engine rooms on ships. The only explanation I can offer is the gland was made up snug to quickly. I found it best to let them leak to much and take up only enough to keep the gland cool and not flood the compartment. In a 4 hour watch I would take up on the gland nuts one flat and make sure the flow was always more than needed to cool the gland. If over tightening and then backing off the packing was compressed but not released in the stuffing box completely so as it ran the adjustment was slightly out, IE packing tight but gland loose. Seemed like the smaller sizes were even more sensitive to this. I don't know if that's what's happening in your case.
Even with the white PTFE and brown flax packing I would grease the snot out of it. Also make sure you got all the old packing rings out as sometimes there's another ring hiding down deep in the bore of the tube.

[sailorboy1]

packing slowly heats up and expands, later when it is cold and slowly dripping deposits slowly collect and stop the flow

[zeehag]

mine stops dripping after a few days due to salt build up.
when engine is running i have slow dripping when i am using teflon packing.
when i use flax packing it always drips unless i am in slip or at anchor a few days when the salt builds up and keeps packing gland from dripping.

[Pete7]

Can you not just fit a volvo seal and be done with it, although you will need a vacuum cleaner to deal with the dusty bilges that will develop instead of oily water.

Pete